In the drive for higher integration and operating speeds in LSI devices, the pattern rule is made drastically finer. The rapid advance toward finer pattern rules is grounded on the development of a projection lens with an increased NA, a resist material with improved performance, and exposure light of a shorter wavelength. To the demand for a resist material with a higher resolution and sensitivity, chemically amplified positive working resist materials that utilize as a catalyst the acid generated upon light exposure are effective as disclosed in U.S. Pat. No. 4,491,628 and U.S. Pat. No. 5,310,619 (JP-B 2-27660 and JP-A 63-27829). They now become predominant resist materials especially adapted for deep UV lithography. Also, the change-over from i-line (365 nm) to shorter wavelength KrF excimer laser (248 nm) brought about a significant innovation. Resist materials adapted for KrF excimer lasers enjoyed early use on the 0.30 micron process, proceeded through the 0.25 micron, 0.18 micron and 0.13 micron rules, and currently entered the mass production phase on the 0.09 micron rule. Engineers have started investigation on the 0.065 micron rule, with the trend toward a finer pattern rule being accelerated.
An ArF excimer laser (193 nm) is expected to enable miniaturization of the design rule to 0.13 μm or less. Conventional novolac resins and polyvinylphenol resins cannot be used as the base resin for ArF excimer laser resists because they have very strong absorption in proximity to 193 nm. To ensure transparency and dry etching resistance, some engineers investigated acrylic and alicyclic (typically cycloolefin) resins as disclosed in JP-A 9-73173, JP-A 10-10739, JP-A 9-230595 and WO 97/33198.
For the ArF resists, substantial line edge roughness is also considered problematic. It is described in Proc. SPIE, Vol. 3999, p. 264 (2000), for example, that image contrast is in inverse proportion to line edge roughness. The higher the light contrast, the less becomes the line edge roughness. For example, increased NA of lens, application of modified illumination or phase shift mask, or wavelength reduction allows the light contrast to be increased and the line edge roughness to be reduced. The wavelength reduction from KrF to ArF excimer laser is expected to reduce line edge roughness. In fact, however, it was reported that ArF resists have greater line edge roughness than KrF resists. This is attributable to the difference in performance between ArF and KrF resists, and remains to be one of outstanding problems for ArF resists. Another problem is that ArF resists have weak etching resistance as compared with KrF resists. In particular, a problem that roughness is developed on the surface after etching and transferred to the substrate as striations is pointed out in Proc. SPIE, Vol. 3678, p. 1209 (1999) and Proc. SPIE, Vol. 5039, p. 665 (2003). It is also reported in Proc. SPIE, Vol. 5039, p. 672 (2003) that a resist using an alternating copolymer as the base forms a pattern with minimal edge roughness after development. The alternating copolymer in which the arrangement of recurring units is controlled to the molecular level is characterized by its ability to minimize edge roughness.